1. Field of the Invention
The present invention relates to a method for manufacturing a piezo-resonator and more particularly to technology being effectively used in the method for manufacturing the piezo-resonator that operates at resonant frequencies being different from one another in particular.
2. Description of the Related Art
When a filter is constructed of a piezo-resonator using a BAW (Bulk Acoustic Wave) that propagates through a piezoelectric film, it is necessary that two or more piezo-resonators are employed which operate at resonant frequencies being different from one another. Generally, this can be achieved by making a film thickness of an upper electrode be varied in each of the two or more piezo-resonators. Moreover, the upper electrode is formed by patterning operations using lithography technology.
Therefore, when a filter having a desired frequency characteristic is formed on a same filter, patterning and frequency adjustment by changing a film thickness are essential in a process of forming an upper electrode.
Here, the patterning to be performed on an upper electrode and its frequency adjustment employed in conventional manufacturing methods of a piezo-resonator are described in Japanese Patent Application Laid-open No. 2002-335141 and Japanese Patent Application Laid-open No. 2003-22074, as will later be described more in detail. Moreover, in the description, it is assumed that the filter is made up of a piezo-resonator that operates at two resonant frequencies (resonant frequencies A and B) being different from one another.
However, the conventional manufacturing methods of a piezo-resonator described in Japanese Patent Applications Laid-open No. 2002-335141 and No. 2003-22074 inevitably need many steps for manufacturing a piezo-resonator that operates at resonant frequencies being different from one another.